Date: Thu, 11 Apr 2024 12:25:40 +0800
From: David Gow <davidgow@...gle.com>
To: Will Deacon <will@...nel.org>
Cc: Naresh Kamboju <naresh.kamboju@...aro.org>, mic@...ikod.net, keescook@...omium.org, 
	rmoar@...gle.com, lkft-triage@...ts.linaro.org, kunit-dev@...glegroups.com, 
	linux-kernel@...r.kernel.org, peterz@...radead.org, mingo@...hat.com, 
	longman@...hat.com, boqun.feng@...il.com, anders.roxell@...aro.org, 
	dan.carpenter@...aro.org, arnd@...db.de, linux@...ck-us.net, 
	Linux Kernel Functional Testing <lkft@...aro.org>
Subject: Re: BUG: KASAN: null-ptr-deref in _raw_spin_lock_irq next-20240410

On Wed, 10 Apr 2024 at 23:23, Will Deacon <will@...nel.org> wrote:
>
> On Wed, Apr 10, 2024 at 03:57:10PM +0530, Naresh Kamboju wrote:
> > Following kernel crash noticed on Linux next-20240410 tag while running
> > kunit testing on qemu-arm64 and qemu-x86_64.
> >
> > Reported-by: Linux Kernel Functional Testing <lkft@...aro.org>
> >
> > Crash log on qemu-arm64:
> > ----------------
> > <3>[ 30.465716] BUG: KASAN: null-ptr-deref in _raw_spin_lock_irq (include/linux/instrumented.h:96 include/linux/atomic/atomic-instrumented.h:1301 include/asm-generic/qspinlock.h:111 include/linux/spinlock.h:187 include/linux/spinlock_api_smp.h:120 kernel/locking/spinlock.c:170)
> > <3>[   30.467097] Write of size 4 at addr 0000000000000008 by task swapper/0/1
> > <3>[   30.468059]
> > <3>[   30.468393] CPU: 0 PID: 1 Comm: swapper/0 Tainted: G    B            N 6.9.0-rc3-next-20240410 #1
> > <3>[   30.469209] Hardware name: linux,dummy-virt (DT)
> > <3>[   30.469645] Call trace:
> > <3>[ 30.469919] dump_backtrace (arch/arm64/kernel/stacktrace.c:319)
> > <3>[ 30.471622] show_stack (arch/arm64/kernel/stacktrace.c:326)
> > <3>[ 30.472124] dump_stack_lvl (lib/dump_stack.c:117)
> > <3>[ 30.472947] print_report (mm/kasan/report.c:493)
> > <3>[ 30.473755] kasan_report (mm/kasan/report.c:603)
> > <3>[ 30.474524] kasan_check_range (mm/kasan/generic.c:175 mm/kasan/generic.c:189)
> > <3>[ 30.475094] __kasan_check_write (mm/kasan/shadow.c:38)
> > <3>[ 30.475683] _raw_spin_lock_irq (include/linux/instrumented.h:96 include/linux/atomic/atomic-instrumented.h:1301 include/asm-generic/qspinlock.h:111 include/linux/spinlock.h:187 include/linux/spinlock_api_smp.h:120 kernel/locking/spinlock.c:170)
> > <3>[ 30.476257] wait_for_completion_timeout (kernel/sched/completion.c:84 kernel/sched/completion.c:116 kernel/sched/completion.c:127 kernel/sched/completion.c:167)
> > <3>[ 30.476909] kunit_try_catch_run (lib/kunit/try-catch.c:86)
> > <3>[ 30.477628] kunit_run_case_catch_errors (lib/kunit/test.c:544)
> > <3>[ 30.478311] kunit_run_tests (lib/kunit/test.c:635)
> > <3>[ 30.478865] __kunit_test_suites_init (lib/kunit/test.c:729 (discriminator 1))
> > <3>[ 30.479482] kunit_run_all_tests (lib/kunit/executor.c:276 lib/kunit/executor.c:392)
> > <3>[ 30.480079] kernel_init_freeable (init/main.c:1578)
> > <3>[ 30.480747] kernel_init (init/main.c:1465)
> > <3>[ 30.481474] ret_from_fork (arch/arm64/kernel/entry.S:861)
> > <3>[   30.482080] ==================================================================
> > <1>[   30.484503] Unable to handle kernel NULL pointer dereference at virtual address 0000000000000008
> > <1>[   30.485369] Mem abort info:
> > <1>[   30.485923]   ESR = 0x000000009600006b
> > <1>[   30.486943]   EC = 0x25: DABT (current EL), IL = 32 bits
> > <1>[   30.487540]   SET = 0, FnV = 0
> > <1>[   30.488007]   EA = 0, S1PTW = 0
> > <1>[   30.488509]   FSC = 0x2b: level -1 translation fault
> > <1>[   30.489150] Data abort info:
> > <1>[   30.489610]   ISV = 0, ISS = 0x0000006b, ISS2 = 0x00000000
> > <1>[   30.490360]   CM = 0, WnR = 1, TnD = 0, TagAccess = 0
> > <1>[   30.491057]   GCS = 0, Overlay = 0, DirtyBit = 0, Xs = 0
> > <1>[   30.491822] [0000000000000008] user address but active_mm is swapper
> > <0>[   30.493008] Internal error: Oops: 000000009600006b [#1] PREEMPT SMP
> > <4>[   30.494105] Modules linked in:
> > <4>[   30.496244] CPU: 0 PID: 1 Comm: swapper/0 Tainted: G    B            N 6.9.0-rc3-next-20240410 #1
> > <4>[   30.497171] Hardware name: linux,dummy-virt (DT)
> > <4>[   30.497905] pstate: 224000c9 (nzCv daIF +PAN -UAO +TCO -DIT -SSBS BTYPE=--)
> > <4>[ 30.498895] pc : _raw_spin_lock_irq (arch/arm64/include/asm/atomic_lse.h:271 arch/arm64/include/asm/cmpxchg.h:120 arch/arm64/include/asm/cmpxchg.h:169 include/linux/atomic/atomic-arch-fallback.h:2055 include/linux/atomic/atomic-arch-fallback.h:2173 include/linux/atomic/atomic-instrumented.h:1302 include/asm-generic/qspinlock.h:111 include/linux/spinlock.h:187 include/linux/spinlock_api_smp.h:120 kernel/locking/spinlock.c:170)
> > <4>[ 30.499542] lr : _raw_spin_lock_irq (include/linux/atomic/atomic-arch-fallback.h:2172 (discriminator 1) include/linux/atomic/atomic-instrumented.h:1302 (discriminator 1) include/asm-generic/qspinlock.h:111 (discriminator 1) include/linux/spinlock.h:187 (discriminator 1) include/linux/spinlock_api_smp.h:120 (discriminator 1) kernel/locking/spinlock.c:170 (discriminator 1))
> >
> > <trim>
>
> It's a shame that you have trimmed the register dump here.
>
> > <4>[   30.511022] Call trace:
> > <4>[ 30.511437] _raw_spin_lock_irq (arch/arm64/include/asm/atomic_lse.h:271 arch/arm64/include/asm/cmpxchg.h:120 arch/arm64/include/asm/cmpxchg.h:169 include/linux/atomic/atomic-arch-fallback.h:2055 include/linux/atomic/atomic-arch-fallback.h:2173 include/linux/atomic/atomic-instrumented.h:1302 include/asm-generic/qspinlock.h:111 include/linux/spinlock.h:187 include/linux/spinlock_api_smp.h:120 kernel/locking/spinlock.c:170)
> > <4>[ 30.512013] wait_for_completion_timeout (kernel/sched/completion.c:84 kernel/sched/completion.c:116 kernel/sched/completion.c:127 kernel/sched/completion.c:167)
> > <4>[ 30.512627] kunit_try_catch_run (lib/kunit/try-catch.c:86)
> > <4>[ 30.513188] kunit_run_case_catch_errors (lib/kunit/test.c:544)
> > <4>[ 30.513801] kunit_run_tests (lib/kunit/test.c:635)
>
> Ok, so 'task_struct->vfork_done' is NULL. Looks like this code was added
> recently, so adding Mickaël to cc.
>

Thanks. This looks like a race condition where the KUnit test kthread
can terminate before we wait on it.

Mickaël, does this seem like a correct fix to you?
---
From: David Gow <davidgow@...gle.com>
Date: Thu, 11 Apr 2024 12:07:47 +0800
Subject: [PATCH] kunit: Fix race condition in try-catch completion

KUnit's try-catch infrastructure now uses vfork_done, which is always
set to a valid completion when a kthread is crated, but which is set to
NULL once the thread terminates. This creates a race condition, where
the kthread exits before we can wait on it.

Keep a copy of vfork_done, which is taken before we wake_up_process()
and so valid, and wait on that instead.

Fixes: 4de2a8e4cca4 ("kunit: Handle test faults")
Reported-by: Linux Kernel Functional Testing <lkft@...aro.org>
Signed-off-by: David Gow <davidgow@...gle.com>
---
lib/kunit/try-catch.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/lib/kunit/try-catch.c b/lib/kunit/try-catch.c
index fa687278ccc9..fc6cd4d7e80f 100644
--- a/lib/kunit/try-catch.c
+++ b/lib/kunit/try-catch.c
@@ -63,6 +63,7 @@ void kunit_try_catch_run(struct kunit_try_catch
*try_catch, void *context)
{
       struct kunit *test = try_catch->test;
       struct task_struct *task_struct;
+       struct completion *task_done;
       int exit_code, time_remaining;

       try_catch->context = context;
@@ -75,13 +76,14 @@ void kunit_try_catch_run(struct kunit_try_catch
*try_catch, void *context)
               return;
       }
       get_task_struct(task_struct);
+       task_done = task_struct->vfork_done;
       wake_up_process(task_struct);
       /*
        * As for a vfork(2), task_struct->vfork_done (pointing to the
        * underlying kthread->exited) can be used to wait for the end of a
        * kernel thread.
        */
-       time_remaining = wait_for_completion_timeout(task_struct->vfork_done,
+       time_remaining = wait_for_completion_timeout(task_done,
                                                    kunit_test_timeout());
       if (time_remaining == 0) {
               try_catch->try_result = -ETIMEDOUT;
--

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